Piles used as foundation for civil engineering and construction structures achieve a supporting force derived from an end supporting force and a frictional force on the outer peripheral surface. The end supporting force is a bearing pressure resistance occurring at an end portion of the pile, which is driven into hard ground to obtain a large supporting force. The frictional force on the outer peripheral surface occurs from a frictional force between the pile and the ground. In general, the frictional force on the outer peripheral surface occurring between the steel pipe pile and the ground is small.
Thus, the large supporting force is obtained by driving the supporting piles until they reach the hard supporting layer, or using long or large-diameter piles to increase the frictional area on the outer peripheral surface. Thus, in the case where the ground is weak or the supporting layer is located deeply in the ground, the size of the pile needs to be increased, resulting in uneconomical design.
In order to address these problems, for example, Patent Document 1 discloses a configuration capable of reaching the piles up to the hard supporting layer, and a recess-provided steel pipe and a composite pile in which the steel pipe needs not to be longer or larger in diameter than necessary. This recess-provided steel pipe and the composite pile have groove portions provided thereto to increase the adhesive force with the ground or solidified material such as concrete, cement, and soil cement in an integrated manner, thereby achieving increased supporting force.
Further, for example, Patent Document 2 discloses a technique of inserting a steel pipe having groove portions formed thereto into a hole formed in the bedrock to fix the bedrock, and inflating the steel pipe.